INTERNATIONAL STANDARD NORME INTERNATIONALE

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1 INTERNATIONAL STANDARD NORME INTERNATIONALE IEC Edition Shunt capacitors for AC power systems having a rated voltage above V Part 4: Internal fuses Condensateurs shunt pour réseaux à courant alternatif de tension assignée supérieure à V Partie 4: Fusibles internes IEC : (en-fr)

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3 INTERNATIONAL STANDARD NORME INTERNATIONALE IEC Edition Shunt capacitors for AC power systems having a rated voltage above V Part 4: Internal fuses Condensateurs shunt pour réseaux à courant alternatif de tension assignée supérieure à V Partie 4: Fusibles internes INTERNATIONAL ELECTROTECHNICAL COMMISSION COMMISSION ELECTROTECHNIQUE INTERNATIONALE PRICE CODE CODE PRIX L ICS ; ISBN Warning! Make sure that you obtained this publication from an authorized distributor. Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé. Registered trademark of the International Electrotechnical Commission Marque déposée de la Commission Electrotechnique Internationale

4 2 IEC :2014 IEC 2014 CONTENTS FOREWORD Scope and object Normative references Terms and definitions Performance requirements General Disconnecting requirements Withstand requirements Tests Routine tests General Discharge test Type tests Disconnecting test on fuses Test procedures Capacitance measurement Inspection of the unit Voltage test after opening the container... 8 Annex A (normative) Test procedures for the disconnecting test on internal fuses... 9 A.1 General... 9 A.2 Test procedures... 9 Annex B (informative) Guide for coordination of fuse protection B.1 General B.2 Protection sequence... 11

5 IEC :2014 IEC INTERNATIONAL ELECTROTECHNICAL COMMISSION SHUNT CAPACITORS FOR AC POWER SYSTEMS HAVING A RATED VOLTAGE ABOVE V Part 4: Internal fuses FOREWORD 1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as IEC Publication(s) ). Their preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory work. International, governmental and nongovernmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for Standardization (ISO) in accordance with conditions determined by agreement between the two organizations. 2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international consensus of opinion on the relevant subjects since each technical committee has representation from all interested IEC National Committees. 3) IEC Publications have the form of recommendations for international use and are accepted by IEC National Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any misinterpretation by any end user. 4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications transparently to the maximum extent possible in their national and regional publications. Any divergence between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in the latter. 5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any services carried out by independent certification bodies. 6) All users should ensure that they have the latest edition of this publication. 7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and members of its technical committees and IEC National Committees for any personal injury, property damage or other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications. 8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is indispensable for the correct application of this publication. 9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent rights. IEC shall not be held responsible for identifying any or all such patent rights. International Standard IEC has been prepared by IEC technical committee 33: Power capacitors and their applications. This second edition cancels and replaces the first edition published in This edition constitutes a technical revision. This edition includes the following significant technical changes with respect to the previous edition: The disconnecting requirements have been modified.

6 4 IEC :2014 IEC 2014 The text of this standard is based on the following documents: FDIS 33/548/FDIS Report on voting 33/561/RVD Full information on the voting for the approval of this standard can be found in the report on voting indicated in the above table. This publication has been drafted in accordance with the ISO/IEC Directives, Part 2. A list of all parts in the IEC series, published under the general title Shunt capacitors for AC power systems having a rated voltage above V, can be found on the IEC website. The committee has decided that the contents of this publication will remain unchanged until the stability date indicated on the IEC web site under " in the data related to the specific publication. At this date, the publication will be reconfirmed, withdrawn, replaced by a revised edition, or amended.

7 IEC :2014 IEC SHUNT CAPACITORS FOR AC POWER SYSTEMS HAVING A RATED VOLTAGE ABOVE V Part 4: Internal fuses 1 Scope and object This part of IEC applies to internal fuses which are designed to isolate faulty capacitor elements, in order to allow operation of the remaining parts of that capacitor unit and the bank in which the capacitor unit is connected. Such fuses are not a substitute for a switching device such as a circuit-breaker, or for external protection of the capacitor bank or any part thereof. The object of this part of IEC is to formulate requirements regarding performance and testing and to provide a guide for coordination of fuse protection. 2 Normative references The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies. IEC :2005, Shunt capacitors for a.c. power systems having a rated voltage above 1000 V Part 1: General 3 Terms and definitions For the purpose of this part of IEC 60871, the terms and definitions in IEC , as well as the following, apply. 3.1 rated voltage of a capacitor element U Ne r.m.s. value of the alternating voltage for which the capacitor element has been designed 4 Performance requirements 4.1 General The fuse is connected in series to the element(s) which the fuse is intended to isolate if the element(s) becomes faulty. The range of currents and voltages for the fuse is therefore dependent on the capacitor design, and in some cases also on the bank in which the fuse is connected. The requirements are valid for a bank or a capacitor switched by restrike-free circuit-breakers. If the circuit-breakers are not restrike-free, other requirements shall be agreed between manufacturer and purchaser. The operation of an internal fuse is in general determined by one or both of the two following factors:

8 6 IEC :2014 IEC 2014 the discharge energy from elements or units connected in parallel with the faulty element or unit; the power-frequency fault current. The additional current and voltage resulting from the blowing of some fuses should be taken into account in the design. 4.2 Disconnecting requirements The fuse shall enable the faulty element to be disconnected when electrical breakdown of elements occurs in a voltage range, in which u 1 = 0,9 2U Ne is the lowest, and u 2 = 2,5 2U Ne is the highest (instantaneous) value of the element voltage at the instant of fault. The range u 1 to u 2 is based on the voltage that might occur across the capacitor element at the instant of electrical breakdown. The u 2 value is of a transient nature, mostly related to switching operations, and some allowance has been made for the extra voltage increase that might occur (before activation of protection) due to earlier disconnection of parallel elements in a series group of elements (See B.1). If the application of capacitors leads to u 1 and u 2 value, other than those indicated, for example for filter capacitors or when the protection settings limit the value of overvoltage, the lower and upper test voltage limits shall be changed according to an agreement between manufacturer and purchaser. 4.3 Withstand requirements After operation, the fuse assembly shall withstand full element voltage, plus any unbalance voltage due to fuse action, and any short-time transient overvoltages normally experienced during the life of the capacitor. Throughout the life of the capacitor, the fuses shall be capable of carrying continuously a current equal to or greater than the maximum permissible unit current divided by the number of parallel fused paths. The fuses shall be capable of withstanding the inrush-currents due to the switching operations expected during the life of the capacitor. The fuses connected to the undamaged elements shall be able to carry the discharge currents due to the breakdown of elements. The fuses shall be able to carry the currents due to short-circuit faults on the bank external to the unit(s) occurring at a peak voltage of 2,5 U N. 5 Tests 5.1 Routine tests General The fuses shall be able to withstand all routine tests of the capacitor unit in accordance with IEC

9 IEC :2014 IEC Discharge test Capacitors having internal fuses shall be subjected to one short-circuit discharge test, from a d.c. voltage of 1,7 U N through a gap situated as closely as possible to the capacitor, without any additional impedance in the circuit (see note). The capacitance shall be measured before and after the discharge test. The difference between the two measurements shall be less than an amount corresponding to one internal fuse operation. The discharge test may be made before or after the voltage test between terminals (see IEC :2005, Clause 9). However, if it is made after the voltage test between terminals, a capacitance measurement at rated voltage shall be made afterwards to detect fuse operation. If, by agreement with the purchaser, capacitors are accepted with operated fuses, the voltage test between terminals (IEC :2005, Clause 9) shall be made after the discharge test. It is permitted that d.c. charging voltage be generated by initially energizing with an a.c. voltage of 1,7 U N peak value and disconnecting at a current zero. The capacitor is then immediately discharged from this peak value. Alternatively, if the capacitor is disconnected at a slightly higher voltage than 1,7 U N, the discharge may be delayed until the discharge resistor reduces the voltage to 1,7 U N. 5.2 Type tests The fuses shall be able to withstand all type tests of the capacitor units in accordance with IEC The unit(s) shall have passed all routine tests stated in IEC A disconnecting test on fuses (see 5.3) shall be performed either on one complete capacitor unit or, at the choice of the manufacturer, on two units, one unit being tested at the lower voltage limit, and one unit at the upper voltage limit, in accordance with Due to testing, measuring and safety circumstances, it may be necessary to make some modifications to the unit(s) under test; for example those indicated in annex A. See also the different test methods given in Annex A. Type tests are considered valid if they are performed on capacitor(s) of a design identical with that of the capacitor offered, or on a capacitor(s) of a design that does not differ from it in any way that might affect the properties to be checked by the type tests. 5.3 Disconnecting test on fuses Test procedures The disconnecting test on fuses shall be performed at the lower a.c. element voltage limit of 0,9 U Ne and at the upper voltage limit of 2,5 U Ne or other values according to an agreement between manufacturer and purchaser If the test is carried out with d.c., the test voltage shall be test voltage. 2 times the corresponding a.c. NOTE Normally the dielectric would only withstand an a.c. voltage of 2.5 U N for a very limited period of time. Therefore a test with d.c. is in most cases to be preferred.

10 8 IEC :2014 IEC 2014 If the test is carried out with a.c., the triggering of the element failure with a voltage peak shall not be necessary for the test at the lower voltage limit. Certain test methods are indicated in Annex A Capacitance measurement After the test, the capacitance shall be measured to prove that the fuses have blown. A measuring method shall be used that is sufficiently sensitive to detect the capacitance change caused by one blown fuse Inspection of the unit Before opening, no significant deformation of the container shall be apparent. After opening the container, a check shall be made to ensure that: a) no severe deformation of sound fuses is apparent; b) no more than one additional fuse (or one-tenth of fused elements directly in parallel) has been damaged (see note 1 to Clause A.1). If method b) given in Annex A is used, note 1 to Clause A.1 shall be observed. NOTE A small amount of blackening of the impregnant will not affect the quality of the capacitor. It should be noted that dangerous trapped charges may be present on elements disconnected either by operated fuses or by damage to their connections. All elements should be discharged with great care Voltage test after opening the container A voltage test shall be carried out by applying a d.c. voltage of 3,5 U Ne (U Ne element voltage) for 10 s across the broken down element and the gap in its blown fuse. The element and the fuse should not be removed from the unit for this test. During the test, the gap shall be in the impregnant. No breakdown over the fuse gap or between any part of the fuse and any other part of the unit is allowed. NOTE For units with all elements in parallel, or in all other cases if test procedure b), c), d), or e) indicated in Annex A is used, this test can be replaced by an a.c. test before the opening of the unit. The test voltage between the terminals is calculated using the capacitance ratio such that the voltage across the breakdown element and the gap in its blown fuse is 3,5 U Ne 2.

11 IEC :2014 IEC Annex A (normative) Test procedures for the disconnecting test on internal fuses A.1 General One of the test procedures a), b), c), d), e) or an alternative method, shall be used. The capacitor voltage and current shall be recorded during the test to verify that the fuse has disconnected correctly. To verify the current-limiting behavior of the fuses when tested at the upper voltage limit, the voltage drop, excluding transient, across the blown fuse shall not exceed 30 %. If the voltage drop exceeds 30 %, precaution shall be taken to make certain that the parallel stored energy and the power-frequency fault current available from the test system are representative of service conditions. A test shall then be made under these conditions to demonstrate satisfactory operation of the fuse. Precautions should be taken when performing this test against the possible explosion of a capacitor unit and the explosive projection of the nail. NOTE At the upper voltage limit, one additional fuse (or one-tenth of the fused elements directly in parallel) connected to a sound element(s) is allowed to be damaged. A.2 Test procedures a) Capacitor preheating The capacitor unit is preheated in a chamber before applying the a.c. test voltage at the lower voltage limit. Preheating temperature (100 C to 150 C) is chosen by the manufacturer to achieve a practical short time (some minutes to some hours) to the first breakdown. To prevent excessive internal liquid pressure due to high temperature, the unit may be equipped with a relief tube including a valve which is closed at the instant of applying the test voltage. A lower preheating temperature may be used when applying the test voltage at the upper voltage limit, in order to avoid breakdowns before reaching the test voltage. b) Mechanical puncture of the element Mechanical puncture of the element is made by a nail, which is forced into the element through a pre-drilled hole in the container. The test voltage may be d.c. or a.c., the choice being left to the manufacturer. If a.c. voltage is used, the timing of the puncture shall be made so that breakdown occurs close to the instant of peak voltage. Puncture of only one element cannot be guaranteed. In order to limit the possibility of a flashover to the container along the nail, or through the hole caused by the nail, the punctures may be performed in the elements connected, permanently or during the test, to the container. NOTE DC voltage is especially suitable for capacitors having all elements in parallel. c) Electrical breakdown of the element (first method) Some elements in the test unit are each provided with, for example, a tab inserted between the dielectric layers. Each tab is connected to a separate terminal.